BP Unfiltered

The Velocity Gainers and Losers of Spring 2013

Two years ago Mike Fast (now with the Houston Astros) took a look at pitchers who gained or lost velocity between the end of 2010 and spring 2011. We won't summarize his whole study here, but here’s the money quote:

There is definitely a predictive relationship between the fastball speed change observed in spring training and the fastball speed change observed in the regular season. Pitchers on average retained 41% of their spring training speed changes into the regular season, and the correlation coefficient for the sample here is r=0.53.

With that predictive relationship in mind, we've compared velocities from September 2012 and March 2013 and come up with some interesting results. This year's study includes World Baseball Classic pitchers, who were all limited in their usage by rule.

First, a summary of gainers and losers:

Total Pitchers

69

Gainers

25

Losers

44

Average Change

-0.4 mph

MPH Change

# of Pitchers

3

1

2

0

1

6

0 to 1

18

-1 to 0

24

-1

14

-2

5

-3

1

Most pitchers didn't change much at all, with 42 guys within one mile per hour of their September velocity one way or the other. There were more losers than gainers (44 to 25), with 20 guys losing at least one mph but only seven gaining that much.

The pitchers listed below each threw at least 20 fastballs or sinkers (combined) in both September 2012 and March 2013 as a starting pitcher. (Pitches thrown in relief by pitchers who also worked out of the bullpen were not considered.) The big table below shows the raw speed numbers and the change between the two periods. In addition, we reran the numbers using Mike's temperature adjustment technique (37 degrees = 1 mph fastball velocity change, baselining from 70 degrees) and recalculated the changes between periods. For sanity's sake we're showing only the raw numbers below, along with the “Delta” and “DeltaAdj”, the latter being based on the adjusted speed numbers.